1. Technical Field
The present invention relates to an anterior ocular segment optical coherence tomographic imaging device and an anterior ocular segment optical coherence tomographic imaging method that take a tomographic image of an anterior ocular segment including a crystalline lens of a subject's eye.
2. Related Art
Examples of ophthalmologic inspection equipment include an optical coherence tomographic imaging device that images a tomography image of an eye (eyeball) of a subject using Optical Coherence Tomography (OCT). The optical coherence tomographic imaging device is roughly classified into a time domain type (TD-OCT) and a Fourier domain type (FD-OCT).
According to TD-OCT, a beam from a light source is divided into a measurement light and a reference light using a beam splitter, and a reference mirror mechanically scan a subject's eye along an optical axis to find the distribution of reflected light intensity along the depth of the subject's eye. FD-OCT is further classified into a spectral domain type (SD-OCT) and a swept source type (SS-OCT). According to SD-OCT, a coherent light coming from an interferometer is resolved into wavelength spectra using a spectroscope consisting of a diffraction grating, detects the wavelength spectrum using a line sensor (eg. CCD camera), and inverse-fourier transform performs on a detection signal to acquire the distribution of reflected light intensity in the depth direction. According to SS-OCT, a spectrum signal is detected by scanning at light frequencies (wavelength) of a light source at high speed and measuring a signal from a photo detector (photodiode) in terms of time, and the inverse-fourier transform performs on this detection signal to obtain the distribution of reflected light intensity in the depth direction.
According to TD-OCT, information at one point with one measurement light can be acquired, while according to FD-OCT, all information in the depth direction with one measurement light can be acquired. Thus, FD-OCT can be greatly reduced time for measurement than TD-OCT. For this reason, FD-OCT is used for anterior ocular segment OCT to enable three-dimensional analysis.
In general, according to OCT, the measurement light one-dimensionally scan the subject's eye to acquire a two-dimensional tomographic image (B-scan), and the two-dimensional tomographic images are repeatedly acquired while displacing the measurement light with respect to the subject's eye to acquire a three-dimensional image (C-scan).
Scanning methods include raster scan and radial scan. According to raster scan, one-dimensional scan (B-scan) is repeated along a horizontally extending scan line while shifting in the vertical direction (C-scan) to take a three-dimensional image of an eyeball (C-scan). This can acquire the tomographic image along each scan line. According to radial scan, one-dimensional scan (B-scan) along a radially-extending scan line (B-scan) is repeated while shifting in the circumferential direction (C-scan). This can acquire the tomographic image along each scan line.
For example, an anterior ocular segment optical coherence tomographic imaging device using such OCT includes a tomographic image acquisition means that acquires a tomographic image of an anterior ocular segment of a subject's eye in a depth direction along a scan line by optical coherence tomography, an imaging means that takes a front image of the subject's eye, and a cornea apex position detection means that detects position of an apex of a cornea of the subject's eye (for example, refer to Japanese Unexamined Patent Publication No. 2009-142313). In recent years, an anterior ocular segment optical coherence tomographic imaging device that can also image a back face of the crystalline lens of the anterior ocular segment has been proposed. This device can determine the degree of an intraocular lens inserted after a surgery of a cataract based on the acquired image of the crystalline lens (for example, refer to International Publication No. 2013/187361).